(1) Field of the Invention
This invention relates to an automatic sewing apparatus for sewing the crotch of unfinished trousers and the like. In the sewing of such trousers, the crotch and both sides are each combined by a cross seam, with a front body into which a right front body and a left front body are formed being overlapped with a back body into which a right back body and a left back body are formed.
(2) Description of the Related Art
FIG. 1 shows a pair of unfinished trousers 99 as an example of sewn products. Right and left front bodies 100a/100b are formed into a front body 100 by stitching a line .alpha., and a right and left back bodies 101a/101b are formed into a back body 101 by stitching a line .beta.. Both lines .alpha./.beta. are formed by a plain seam (Federal Standard No. 751a Seam Type SSa). The front and back bodies have been combined by seaming both sides, only the crotch .gamma. being left unsewn.
Conventional auto sewing apparatuses for sewing the crotch .gamma. of a pair of unfinished trousers comprise a table 102, a sewing mechanism unit 103, a first hand 104, a second hand 105, and a third hand 106 as shown in FIG. 2 (Refer to Japanese Laid-open Patent Application No. 2-277491 and Japanese Laid-Open Utility Model No. 3-7374).
The sewing mechanism unit 103, like an ordinary sewing machine, comprises a needle, a presser foot, a cloth feed mechanism unit, and a thread cutter.
The first hand 104 includes a guide mechanism unit having a guide edge having a certain angle. The hand 104 guides the trousers 99 to the sewing mechanism unit 103 by holding the bottom of a leg of the trousers 99 on the table 102, with a pair of edges extending from the bottom of one leg to the center of the crotch being overlapped.
The second hand 105 includes a hold mechanism unit for holding the crotch, with the above-mentioned a pair of the edges including the ends A/B of the stitching lines .alpha./.beta. being overlapped, as well as a follow mechanism unit for following the trousers 99 transferred by the sewing operation of the sewing mechanism unit 103. The hold mechanism unit keeps holding the trousers 99 until the second hand 105 moves to a position just before the sewing mechanism unit 103 in the direction of the arrow in FIG. 3. The hand 105 includes a guide mechanism, as the first hand 104, which guides the trousers 99 to the sewing mechanism unit 103 by holding the bottom of the other leg of the trousers 99, with a pair of edges extending from the center of the crotch to the bottom of the other leg being overlapped.
The third hand 106 having almost the same construction as the second hand 105 holds the bottom of the other leg of the trousers 99 and follows the trousers 99 transferred in the direction of the arrow by the sewing operation of the sewing mechanism unit 103.
However, such conventional auto sewing apparatuses have some problems: when such trousers are sewn, a total of six layers of cloth should be sewn together in the intersecting portion of the line .alpha., the line .beta., and the crotch .gamma., which often damages the apparatus or deteriorates the quality of finished products.
As shown in FIG. 4, the above six layers of cloth results from the standing end A of the right/left front bodies 100a/100b being folded down in the same direction as the end B of the right/left back bodies 101a/101b by a presser foot 110.
Although the stitching line over the six-layered cloth is rather short, it may still damage the sewing mechanism unit 103 because the load applied on it is suddenly increased by the tripled thickness, compared to the other portions.
Furthermore, after the end A is folded down, if the transfer of the cloth is checked by the force of the presser foot 110, the ends A and B slip from each other in the sewing direction. Consequently, in a pair of finished trousers, as shown in FIG. 5, the stitching line .alpha. of the front body and the line .beta. of the back body do not overlap, resulting in bad appearance and uncomfortable fitting.
The hold mechanism unit of the second hand 105 is useless to prevent such cloth slipping because it holds the trousers 99 only until the ends A/B are transferred to just before the sewing mechanism unit 103 as previously mentioned.
The slipping may be prevented by intensifying the cloth transfer force of the upper feed dog 111 of the sewing mechanism unit 103 more than the resistance of the presser foot 110. However, this can not be carried out to prevent cloth from being spoiled.